People should, don’t get me wrong, respect the marks of open source projects. If I were reselling a commercial fork of an open source project Foobar, I would not be comfortable putting “FB” or “Foobar” in the name. I’m honestly on board with the Apache Foundation guidelines, where you’re not even supposed to say that Foobar is what you’re selling - it’s a proprietary service with a proprietary name which happens to be powered by Foobar.

But the idea of an enforceable trademark right to stop people from accurately describing their derivative services is another thing where people often don’t want to hear the clear answer. Companies typically go much further than what’s actually required to avoid infringement, because frustrating the open source community you depend on isn’t worth the relatively modest benefits. The Wordpress dynamic is different, because their mark is already licensed to a commercial vendor and already causes routine confusion in that context.